I have a large XML file (about 10K rows) I need to parse regularly that is in this format:
10000
I'd recommend using a SAX parser rather than a DOM parser for a file this large. Nokogiri has a nice SAX parser built in: http://nokogiri.org/Nokogiri/XML/SAX.html
The SAX way of doing things is nice for large files simply because it doesn't build a giant DOM tree, which in your case is overkill; you can build up your own structures when events fire (for counting nodes, for example).